The present invention seeks to substantially reduce the forces acting on the crankcase during engine operation. These forces (tension and/or pressure forces) are caused by the considerable ignition forces in the cylinder and inertia forces of the crankshaft. By relieving the forces acting on the crankcase, it is intended to advantageously reduce the required thickness of the walls of this housing part and also to enable the walls to accommodate openings or bores in addition to the bearing openings for the crankshaft, for example bearing points for the elements disposed in the crankcase for balancing inertia forces of the moving engine parts.
According to the present invention there is provided an internal combustion engine having housing parts forming a cylinder, cylinder head and crankcase, which are made of light metal, wherein a plurality of tightening screws are provided for securing the parts into a single engine block, which screws are disposed substantially parallel to the cylinder axis and pass through the cylinder head and cylinder, and wherein the heads of the screws are seated on the cylinder head, and their threaded ends engage in tapped holes in the crankcase, and further comprising at least two steel tie rods, each of which has a head at one end, which head has a threaded opening, and which tie rods are cast with the crankcase so as to be integral therewith and in such a way that a tie rod is provided on each side of a bearing opening for the crankshaft in the crankcase, which tie rod extends substantially through the entire crankcase, has its longitudinal direction substantially parallel to the cylinder axis, and its threaded opening serving to accommodate the threaded portion of a tightening screw.
The tie rod may readily be dimensioned in such a way that it absorbs the above-mentioned forces acting on the crankcase to a large extent, and hence greatly reduces the forces acting on the housing.
According to an advantageous feature of the present invention, the head of the tie rod is in the form of a hexagon, so as to prevent the tie rod from rotating during casting and tightening.
According to yet another advantageous feature of the present invention, a plurality of circumferential ribs are formed along the tie rod and serve to hold it in the crankcase and to transfer forces, which develop during engine operation, from the crankcase to the tie rod. Advantageously, the circumferential ribs are distributed in the longitudinal direction of the tie rod in such a way that the number thereof is related to the magnitude of the forces associated with the part of the crankcase which surrounds the ribs.